This invention relates to a device for attachment of an aircraft engine onto a nacelle stub fixed to an element of the aircraft structure such as the wing or fuselage.
More precisely, the invention relates to an attachment device designed to transmit lateral and vertical forces from the engine (these force directions are applicable to the case in which the attachment device is fixed under the wing), and the engine torque, to the aircraft structure through the nacelle stub.
Engines installed on aircraft are suspended under the wings or are attached to the side of the fuselage by means of an element called an xe2x80x9cengine nacelle stubxe2x80x9d. This element is called the xe2x80x9cnacelle stubxe2x80x9d throughout the rest of this text for simplification purposes.
The connection between the engine and the nacelle stub is usually made by two or three complementary attachment devices that perform separate functions.
The function of one of these attachment devices is to resist lateral and vertical forces generated by the engine, and the engine torque, in order to retransmit them to the aircraft structure through the nacelle stub. The invention relates particularly to this attachment device. Note particularly that a device of this type can be installed indifferently behind or in front of the engine, with the dimensions of the component parts being adapted accordingly.
As illustrated particularly in documents U.S. Pat. Nos. 5,620,154 and 5,275,357, some existing attachment devices comprise a main attachment structure and an emergency attachment structure. The main attachment structure transmits forces during normal operation, in other words when all parts of the attachment device are intact. The emergency attachment structure is provided to guarantee that the function to transmit forces between the engine and the aircraft is working at all times if one of the parts of the main attachment structure breaks. Thus, it makes it impossible for the engine to fall off.
In these existing attachment devices, the main attachment structure normally comprises a fitting fixed to the nacelle stub, for example by means of screws, and at least two swivel ended connecting rods making the connection between the fitting and the engine. The swivel mounted assembly of the connecting rods onto the fitting and onto the engine makes it impossible for the device to resist forces oriented along the longitudinal axis of the engine. This assembly also compensates for thermal expansion of the engine and maintains the simply supported nature of the connection between the nacelle stub and the engine.
As also illustrated in documents U.S. Pat. Nos. 5,620,154 and 5,275,357, when the existing attachment devices comprise emergency attachment structures, they usually include additional elements such as one or more additional connecting rods inserted between the fitting and the engine. These additional elements have clearances such that normally they do not resist any force when the parts of the main attachment structure are intact and consequently are capable of fulfilling their functions.
Some existing attachment devices such as those used in Airbus programs comprise an intermediate part inserted between the nacelle stub and the fitting. This intermediate part has a trapezoidal cross section and a first plane surface designed to be fixed, for example by four screws, onto an inclined attachment plane of the nacelle stub and a second horizontal plane surface to which the fitting is attached, for example by means of four other screws. The intermediate part may be a single piece or it may be composed of two half pieces assembled together by screws. Its presence contributes to making the attachment device complicated, heavy and large.
In existing attachment devices like those described in documents U.S. Pat. Nos. 5,620,154 and 5,275,357, the additional elements formed by the emergency attachment structure are always inserted between the fitting on the main attachment structure and the engine. In other words, these additional elements are used to conserve the integrity of the engine attachment when the connection between the fitting and the engine is involved. On the other hand, they are incapable of maintaining this integrity when the failure is at the link between the nacelle stub and the fitting, in other words for example the attachment screws or the intermediate part between the nacelle stub and the fitting, when there is an intermediate part.
One solution for maintaining the integrity of the connection between the nacelle stub and the fitting consists of oversizing the attachment screws inserted between the nacelle stub and the intermediate part, and between the said part and the fitting. The valid screws are sized to transmit the forces if one of the screws or one of the half parts forming the intermediate part should fail. However, this solution requires the use of special non-standard clamping tools that have to be kept on board the aircraft, which introduces an undesirable additional weight.
Furthermore, document FR-A-2 770 486 describes a device for attachment of an engine onto an aircraft nacelle stub, designed to maintain the integrity of the engine attachment even in the case of a failure of the fitting on the main attachment structure. This attachment device comprises a main attachment structure of a known type and an emergency attachment structure capable of connecting the nacelle stub to the engine directly without passing through the fitting if the fitting fails. The transmission of forces between the engine and the aircraft is then maintained. Furthermore, the solution described in this document eliminates the need for the presence of the intermediate part, thus making the attachment device absolutely safe.
The purpose of the invention is a device for attachment of an engine on an aircraft nacelle stub, designed to protect the integrity of the engine attachment even following a failure of a half-fitting of the main attachment structure or the means of attachment of the half-fitting on the nacelle stub, while eliminating the need for the presence of the intermediate part.
According to the invention, this result is achieved by a device for attachment of an engine onto an aircraft nacelle stub, the device comprising a main attachment structure capable of transmitting forces between the engine and the nacelle stub during normal operation, and an emergency attachment structure that does not transmit any force during normal operation, the main attachment structure comprising a fitting consisting of two half-fittings, attachment means to fix each of the half-fittings to the nacelle stub separately, and at least two swivel ended connecting rods to connect the fitting to the engine, characterized in that the emergency attachment structure is arranged so that it will transmit the said forces to the other half-fitting if one of the half-fittings or the means of attaching the half-fittings to the nacelle stub should fail.
Since the emergency attachment structure connects the nacelle stub to the engine through the sound half-fitting, the connection between the nacelle stub and the engine is maintained entirely even if a half-fitting or the attachment means associated with the half-fitting should fail. Forces are continuously transmitted between the engine and the aircraft, and the engine cannot fall off, regardless of the cause of the failure (cracks, oxidation, material defects, etc.).
Furthermore, the integrity of the link between the fitting and the engine may be maintained by any of the means used in existing emergency attachment structures.
In one preferred embodiment of the invention, the emergency attachment structure comprises a hinge pin with an axis approximately parallel to the longitudinal axis of the engine, the said hinge pin being fixed to one of the parts composed of the fitting and the nacelle stub and passing through a hole formed in the other part with a clearance during normal operation.
Advantageously, the hinge pin is then fitted to a double hinge fitting that may itself be fitted to the nacelle stub, and the hole passes through the parts of the two half-fittings that fit into the said hinge fitting.
In this case, the double hinge fitting is preferably fixed to the nacelle stub by welding.
More precisely, each of the half-fittings can then be fixed by the said attachment means, onto a surface of the nacelle stub facing the engine, and the double hinge fitting projects towards the engine from the said surface.